Beam convergence system for tri-color kinescope



A. W. FRIEND Dec. 6, 1955 BEAM CONVERGENCE SYSTEM FOR TRI-COLORKINESCOPE Filed July 8, 1953 nited States Patent Cflce Y 2,726,355Patented Dec. (i, 1195.5.

BEAM- CONVERGENCE SYSTEM FOR KIESCOPE Albert W. Friend, Bala-Cynwyd,Pa., assigner to Radio Corporation of America, a corporation of DelawareTRT-COLOR This invention relates` to systems for controlling theelectronbeam energy. ofxcathode ray tubes. It pertains particularly to thecontrol of a. plurality of electron beam components usedf in televisionkinescopesV so as to effect substantial convergence of the components atall points of a raster scanned at a. target electrode.

One type of cathode. ray tube inl which there is encountered theprobleml of maintaining substantial convergence of a plurality of beamcomponents at a target electrode is a color kinescope, such as thatdisclosed in a paper by H. B. Law titled A Three-Gun Shadow-Mask ColorKinescope publishedin the Proceedings of the IRE, vol. 39, No. 10,October 1.951 at page 1186.. Such .a tube hasa luminescentY screenconsisting of a multiplicity of phosphor areas of sub-elementaldimensions. Dilerent ones of the phosphor areas are capable of producinglight of the component image colors when excited by electron beamenergy. In this tube, the different lightproducing phosphor areas areexcited respectively by a plurality of electron beams, orv by aplurality of components ofV a single beam, approaching the screen fromdifferent angles through an apertured electrode. Color selection issecured by the angle at which the electron beam components approach thescreen. A tube of vthe kind described forms the subject matter of U. S.VPatent 2,595,548 granted` May 6, 1952, to Alfred C. Schroeder forPicture Reproducing Apparatus. The-expression electron beam componentsas used in` this specification and claims will be understod to denotethe phosphor-exciting electronic energy produced either by a single, orby a plurality of, electron guns. This ener-gy may be continuous orpulsating as, required` without departing from the scope of theinvention. An example ofv a color kinescope in which differentcomponents of a single electronbeam are used to excite a phosphor screenof the kind described-is disclosed in a paper by R. R. L aw, titled AOne-GunShadoW-Mask Color Kinescope publishedin the Proceedings of theIRE, vol. 39, No. 10, October 1951, at` page 119,4.. Such a tube formsthe subject matter` of a copcnding U. S. application of Russell R. Law,Serial No. 165,552; filed June 1,-1950 and titled Color `TelevisionReproducing Tube.

The successful operation of a multi-color kinescope of the-type referredto requires that the plurality of electron beam` componentsbe made toconverge substantially at the `apertured electrode at all points in thescanned raster. In View of the fact that the different points of such atarget-electrodeare at different distances from the point or regionpofthe electron` beam deflection, it is necessary to provide afield-producing means which is variably energized to producerthe desireddynamic convergence control. One such electron beam` control systern isdisclosed in a paper byAlbert W. Friend titledv Deflection andConvergence in Color Kinescopes published in the Proceedings of the IRE,vol. 39, No. l0,

October 1951` at page 1249. Such a system forms the subjecnmatter of-acopending U, S. application of Albert W. Friend, Serial No. 164,444, flledl/lay 26, 195,0,.and.' titled Electron Beam Control System. In thesystemV disclosed in this copending Friend application, electronopticalapparatus is energizedV both statically and dynamically to produce thedesired result. By means including the static energization of. theelectron-optical apparatus, the Friend systemk referred to eiects.initialV convergence of the electron. beam components substantially atthe center of the raster to be scanned. The dynamic energizationv of.the elect-ronfopticali apparatusr is. effected as functions of bothl thehorizonal andv vertical beamV deflection. Ideally these functions aregenerally parabolic. However, somewhat complicated apparatus often isyre,- quired to produce the desired energizing waveforms.

Therefore, it is an objectz of this invention toA prox/.ide an improvedand simplified electron. beam control system for multi-beam kinescopes.

Another object of.- the. invention is to provideelectromagnetic beamconvergence apparatus whichmay. be energized in a unique manner fromhthe beam deflection apparatus in orderv to effect substantialconvergence of a plurality of electron beam components in all` partszofa raster scanned thereby.

The electron beam convergence system in accordance with the presentinvention is: primarily for use in. conjunction with a cathode rayimage-reproducing tube wherein a plurality ofelectron beam componentswhich traverse predeilection` pathsv that are spaced respectively aboutthe longitudinal' axis of the tube are angularly deflected bothhorizontally and vertically to scanv a raster at a target electrode.Thebeam convergence systemcomprises at least one double magnetic lenssystem. Where only one such` lens system is used, it. may be energizedat either the horizontal. or vertical deflection frequency. ln the eventthat two-such double'magnetic lens systems are employed, they may beenergized.respectivelyy at the horizontal and. vertical deflectionfrequencies. The lens systems are located adjacent to the predeectionpaths of the beams. The field produced by the respective, components ofeach of the double magnetic lens systems extend substantiallylongitudinally of the tube axisbut-.in opposite directions. Byarrangingthese field components in opposite polarities, the individualtendencies, to rotate the beam components about the longitudinal axisof'the tubeare cancelled. The energization V of the doubleelectromagnetic lens systemsin accordance with this.: invention iseffected by rectifying the deection currentsV ernployed to energize theraster scanningv beam deflection yoke. The rectified-deflectioncurrentsarerfurther shaped and combined with a uni-directional componentand impressed upon the double magnetic lens system for-the energizationthereof.`

The novel features. that are considered characteristic of this inventionare set forth with particularity ,inl the appended claims. The inventionitself, however,v both as to its organization andmethod of operation,asV well as additional objects andA advantages thereof, will best beunderstood from the following description when read in connection withthe accompanying drawing.

The single figure of the accompanying drawing is a circuit diagram,mostly in block form except'for'the illustrative details of theapparatus, embodying the present invention for effecting theconvergenceof a plurality of electron beam components atall points in araster scanned in a predetermined'plane.

Reference rstwill be made to Figure 1 ofthe drawings for a descriptionof an illustrative embodiment of the invention. They television receiverrepresented in this-figure is generally'conventional and includes anantenna 11 to which is coupled a conventional television signal receiver12. It willV be` understoodl thatV the receiver 12 may include.. suchusual apparatus as carrier wave amplifiers: atl bothVv radio andintermediate'frequencies, a frequency converter and a carrier wavedemodulator or signal detector. Accordingly, it will be understood thatthere are derived from the receiver 12 a composite television signalincluding the video and synchronizing signal components. The compositetelevision signal, including the video signal component, which isderived from the receiver 12 is impressed upon a video signal channel13. Also, this signal including the synchronizing signal component, isimpressed upon a sync signal separator 14. The video signal channel iscoupled to the usual electron beam control apparatus, customarilyreferred to as electron gun apparatus (not shown), of animage-reproducing device such asa kinescope 15.

In the illustrative embodiment of the invention, it is assumed that theinvention is used in a color television system. In this case, thekinescope may be of the same general type disclosed in the H. B. Lawpaper previously referred to. It will be understood, however, that thekinescope alternativelymay be of other types, such as that shown in theaforementioned R. R. Law paper. In any case, however, the kinescope hasa substantially llat luminescent screen 16 which is provided with amultiplicity of small phosphor areas arranged in groups and capablerespectively of producing light of the different primary colors in whichthe image is to be reproduced when excited by electron beam energy. Inback of, and spaced from the screen 16, there is an apertured maskingelectrode 17 having an aperture for, and in alignment with, each groupof phosphor areas of the screen 16. As previously indicated, thekinescope will be understood to have electron gun apparatus by which todevelop respective electron beams 18, 19 and 20 which are caused toapproach the target electrode structure, including the luminescentscreen 16 and the masking electrode 17, from three different angleswhich, for convenience, have been shown greatly exaggerated in thedrawing. By means of thev different angles of approach these beams arecaused to excite the different colored light-producing phosphors.

The color kinescope also is provided with apparatus by which to deflectthe plurality of electron beam components 18, 19 and 20 both verticallyand horizontally to scan a substantially rectangular raster at theluminescent screen 16. For this purpose, the deflection apparatusincludes a yoke 21 which, in general, is of a conventional type. Itconsists of a pair of interconnected coils 22 and 23 forming ahorizontal deflection winding, and another pair of coils 24 and 25forming a vertical deflection winding. The yoke is mounted around'theneck of the kinescope 15 in the region adjacent to the point at whichthe neck joins the conical sectionV of the tube. The horizontal winding22-23 and the vertical winding 24-25 of the yoke are energized bysubstantially conventional apparatus.

The yoke energizing apparatus includes horizontal Vand verticaldeflection wave sources 26 and 27, respectively, which are coupled tothe synchronizing signal separator 14. The sync signal separator, whichmay be of the type disclosed in U. S. Patent 2,207,775 granted July 16,1940, to A. V. Bedford, separates the synchronizing signals from thevideo signals and also from one another to produce horizontal andvertical frequency synchronizing signals respectively in its outputcircuits H and V. As indicated, these circuits are coupled to theassociated deflection wave sources. It will be understood that each ofthe deflection wave sources 26 and 27 includes the usual apparatus bywhich suitable deflection waves at the horizontal and verticalfrequencies are deevloped for impression upon the deflection yokewindings as described.

In accordance with the present invention, the beam convergence apparatusincludes two double magnetic lens systems, one for energization at thehorizontal deflection frequency and the other at the vertical deflectionfrequency. These two lens systems are shown diagrammatically for clarityand convenience of illustration. The horizontal frequency doublemagnetic lens system 28 in- 4 cludes two coils 29 and 30 coaxiallymounted relative to the neck of the kinescope 1S. The two coils 29 and3() are shown serially connected and are indicated as having the samenumber of turns and as being wound in opposite directions. Accordingly,the traversal of the two coils of the horizontal convergence magneticlens system 28 by the same current will effectively produce two axialmagnetic fields of substantially the same magnitude but of oppositepolarity in the region of the predeflection paths of the electron beamcomponents 18, 19 and 20. Similarly, there is provided a verticalfrequency convergence double electromagnetic lens system 31 mountedaround the neck of the kinescope 15. The vertical convergence magneticlens system 31 also comprises two substantially identical coils 32 and33 wound in opposite directions and serially connected for energizationby the same current wave.

It is seen that, ,by providing apparatus, such as the two coils of eachof the convergence magnetic lens systems, by which to produce axialmagnetic fields of opposite polarity and of the sam'e magnitude, anyrotational effect produced upon the electron beam components by one ofthese coils is cancelled or overcome by a substantially equal andopposite rotational effect produced by the other coil. The netrotational effect upon the electron beam components by either or both ofthe convergence magnetic lens systems 28 and 31 is effectively zero.Hence, the electron beam components 18, 19 and 20 will have the samerelative positions in the region of the target electrode, including theluminescent screen 16, as they would have in the absence of thedescribed electromagnetic lens systems for effecting beam convergence.

In accordance with another feature of the present invention, theconvergence magnetic lens systems 28 and 31 are energized by wavesderived directly from the beam deflection apparatus. To achieve thisresult, the primary windings 34 and 35 respectively of transformers 36and 37 are connected in series with the respective horizontal andvertical deflection windings 22-23 and 24-25 of the deflection yoke 21.Full Wave rectification of these substantially sawtooth yoke currents iseffected by means including double diodes 38 and 39 connectedrespectively to the secondary windings 40 and 41 of the transformers 36and 37.

The output of the horizontal deflection frequency rectifier includingthe double diode 38 is impressed upon the terminals of the horizontalconvergence magnetic lens system 28. Similarly, the output of thevertical deflection frequency rectifier, including the double diode 39,is impressed upon the terminals of the vertical convergence magneticlens system 31. Each of these convergence magnetic lens systems isshunted by suitable wave shaping circuits and amplitude controllingapparatus. In the case of the horizontal convergence magnetic lenssystern 28, the coils 29 and 30 are shunted by a series arrangement of avariable resistor 42 and a capacitor 43. By means of this apparatus, thedesired wave shape which, as described is generally parabolic, may beeffected and adjusted as required by means of the variable resistor 42.There also is provided a shunting inductor 44 which also is of avariable character for the purpose of adjusting the amplitude of thedynamic convergence wave at horizontal frequency which is impressed uponthe lens system 28.

The vertical convergence magnetic lens system 39 also is provided withsimilar apparatus including a variable resistor 45 and a seriesconnected capacitor 46 connected in shunt with the coils 32 and 33 forwave shaping purposes. Also, a variable inductor 47 is shunt connectedfor the purpose of controlling the amplitude of the vertical dynamicconvergence wave.

The apparatus in accordance with the present invention also includesfacilities for effecting the initial or static convergence of theelectron beam components 18, 19 and 20 at a predetermined point in theraster, such as the center thereof. This beam convergence is eected byproviding suitable connections of a pair of terminals 48 to a source ofuni-directional energy such as indicated. Potentiometers 49 and 50associated with the horizontal convergence magnetic lens system 28 andpotentiometers 51 and 52Y associated with the vertical convergencemagnetic lens system 31 are connected in series to the D. C. sourceterminals 48. The potentiometers 49 and 50 are used to adjust the staticenergization of the horizontal magnetic lens system 28 for effectinginitial convergence of the electronV beam components. In a like manner,the potentiometers 51 and 52 are employed to eifect the desired staticenergization of the vertical convergence magnetic lens system 31. Acapacitor 53 connected between the potentiometers 49 and 50 effectivelybypasses dynamic energy at the horizontal deection frequency. Similarly,a capacitor 54 connected between the potentiometers 51 and 52 serves toby-pass vertical deection frequency components around thesepotentiometers.

It may be seen from the foregoing description of an illustrativeembodiment of the invention that there is provided relatively simpleapparatus by means of which to eect both static and dynamic convergenceof a plurality of electron beam components which traverse predeectionpaths that are spaced about the longitudinal axis of the tubesubstantially in the plane of a target electrode. Furthermore, theapparatus in accordance with the invention is energized in a uniquemanner by rectifying the substantially sawtooth deiiection currents forimpression upon the magnetic beam convergence apparatus. By this means,it is not necessary to develop waves of the desired shape at arelatively low level and to amplify such low level signals suitably forexcitation of the magnetic lens apparatus. The amplification of waves ofsuch complex form is not as simple as the high level rectification ofthe deflection waves in accordance with the present invention.

Having set out the character of the invention in the foregoingdescription, its scope is defined in the appended claims.

What is claimed is:

l. In a cathode ray tube image-reproducing system wherein, a pluralityof electron beam components, which traverse predeflection paths that arespaced respectively about the longitudinal axis of the tube, areangularly deflected by electromagnetic apparatus both horizontally andvertically to scan a raster at a target electrode, an electron beamconvergence system comprising, a double magnetic lens system energizableto produce axial fields of similar magnitude but of opposite polarityfor traversal by said beam components, rectifier means coupled to saidbeam deflection apparatus to produce a convergence control wave, andmeans coupling said rectifier means and said lens system to energizesaid lens system by said convergence control wave.

2. In a cathode ray tube image-reproducing system wherein, a pluralityof electron beam components, which traverse predeflection paths that arespaced respectively about the longitudinal axis of the tube areangularly deected by electromagnetic apparatus both horizontally andvertically to scan a raster at a target electrode, an electron beamconvergence system comprising, a double electromagnetic lens systemenergizable to produce axial fields of similar magnitude but of oppositepolarity for traversal by said beam components, rectifier meansincluding a transformer having a winding coupled to said beam deectionapparatus for traversal by sawtooth wave current at one of said deectionfrequencies to produce a convergence control wave at said one defiectionfrequency, and means coupling said rectifier means and said lens systemto energize said lens system by said convergence control wave.

3. In a cathode ray tube image-reproducing system wherein, a pluralityof electron beam components, which traverse predeection paths that arespaced respectively about the longitudinal axis of the tube, areangularly deflected by electromagnetic apparatus both horizontally andvertically to scan a raster at a target electrode, an electron beamconvergence system comprising, two double magnetic lens systems, eachseparately energizable to produce respective pairs of axial fields fortraversal by said beam components, the fields of each of said pairs ofaxial fields being of similar magnitude but of opposite polarity,horizontal and vertical frequency rectifier means coupled respectivelyto said horizontal and vertical deflection apparatus to producehorizontal and vertical frequency convergence control waves, and meanscoupling said horizontal and vertical rectifier .means respectively tosaid two double magnetic lens systems to energize said lens systems bysaid respective convergence control waves.

4. In a cathode ray tube image-reproducing system wherein, a pluralityof electron beam components, which traverse predeection paths that arespaced respectively about the longitudinal axis of the tube, areangularly deflected by electromagnetic apparatus both horizontally andvertically to scan a raster at a target electrode, an electron beamconvergence system comprising, a beam deection yoke having horizontaland vertical windings, means including respective sources of sawtoothwaves at horizontal and vertical deflection frequencies coupled to saidyoke for energizing said respective horizontal and vertical windings, adouble magnetic lens system energizable to produce axial elds of similarmagnitude but of opposite polarity for traversal by said beamcomponents, rectifier means coupled to one of said deflection yokewindings to produce a convergence control wave, and means coupling saidrectifier means and said lens system to energize said lens system bysaid convergence control wave. Y

5. An electron beam convergence system as dened in claim 4 wherein, saidrectifier means includes a transformer having a winding connected inseries with one of said defiection yoke windings.

6. In a cathode ray tube image-reproducing system wherein, a pluralityof electron beam components, which traverse predeection paths that arespaced respectively about the longitudinal axis of the tube, areangularly deflected by electromagnetic apparatus both horizontally andvertically to scan a raster at a target electrode, an electron beamconvergence system comprising, an electron beam deflection yoke havinghorizontal and vertical windings, means including source of sawtoothwaves respectively having horizontal and vertical deflection frequenciescoupled to said yoke windings for energizing said yoke, two doublemagnetic lens system each separately energizable to produce respectivepairs of axial fields for traversal by said beam components, the fieldsof each of said pairs of axial fields being of similar magnitude but ofopposite polarity, two rectifier means coupled respectively to saidhorizontal and vertical yoke windings to produce respective convergencecontrol waves at horizontal and vertical defiection frequencies, andmeans coupling said respective rectifier means and said two doublemagnetic lens systems to separately energize said two lens systems bysaid respective convergence control waves at horizontal and verticaldeflection frequencies.

7. An electron beam convergence system as Vdefined in claim 6 wherein,each of said last-named coupling means includes a resistive-capacitivewave-shaping network.

8. An electron beam convergence system as delned in claim 6 wherein,each of said last-named coupling means includes a variable amplitudedetermining inductor.

References Cited in the le of this patent UNITED STATES PATENTS2,220,303 Tingley NOV. 5, 1940 2,539,492 Smyth Ian. 30, 1951 `2,579,014Schlesinger Dec. 18, 1951

